This invention relates to abrasive articles and to their preparations. In particular, the invention relates to abrasive articles of the type comprising a fabric material, discrete areas of electro-deposited metal extending on or through and carried by the fabric material, and having abrasive material embedded in the metal.
The preparation of electro-deposited abrasive layers through a fabric material is known in the art and disclosed, for example, in British Patent No. 2 200 920, European Patent No. 13486 and U.S. Pat. No. 4,256,467, amongst others. Generally, the abrasive layer is formed by laying a length of fabric, for example, a woven or non-woven mesh material, onto an electrically conducting surface and electro-depositing a metal onto the fabric material in the presence of an abrasive mineral such that the mineral becomes embedded in the metal. An insulating material is selectively applied to the fabric material or to the electrically conducting surface before deposition of the metal layer so that the metal can only deposit onto the fabric in those areas not covered by the insulating material, thereby defining the pattern of the abrading surface.
In one method of making an electro-deposited abrasive layer, a mesh material in the form of a woven fabric of electrically insulating material such as nylon, cotton, terylene, or the like, is screen printed with insulating material in the form of ink. The ink is ordinarily waterproof and acid resistant and in its preferred form is colour fast at elevated working temperatures of the abrasive article, for example, up to approximately 220xc2x0 C. The ink should be compatible with any hot-melt adhesive, which may subsequently be applied to the abrasive layer to secure it to the backing material. The ink may be a resin based or oil based ink and coloured as desired.
The screen-printing may be conducted by conventional screen printing techniques in such a manner to ensure that the ink penetrates into and is absorbed onto defined areas of the fabric material leaving discrete areas without any insulating material, which defines the abrasive surface. Such discrete areas may be of any convenient shape and size, for example, circular, diamond-shaped, rectangular, etc.
In another method, an electrically insulating mask is applied to an electrically conducting surface, for example, a stainless steel drum, the fabric material laid on the electrically conducting surface, and metal electro-deposited through the fabric material in the presence of abrasive material to provide the discrete areas of metal containing abrasive material.
In a further method, an ink may be combined with an adhesive and screen-printed onto the fabric material. The metal is deposited, as described previously, and the resulting abrasive layer may be applied to a backing material by heating the abrasive layer to melt the adhesive content of the insulating material, thereby adhering the backing material to the abrasive layer.
In another method, instead of the insulating material being an ink, or an ink and adhesive combination, adhesive only may be used as the insulating material. In this case, the adhesive may be in the form of a sheet, which is applied to the fabric material before electro-deposition. Usually the adhesive sheet will be perforated and thereby formed with a plurality of openings of the desired shape and size before application to the fabric material. Preferably, this perforation will be by cutting out the openings from the sheet by any convenient means.
The adhesive sheet is then heated when in contact with the fabric material and pressure is applied to cause the adhesive to absorb and enter the spaces in the fabric material. When fully penetrated, the fabric material is cooled.
The fabric material is then electro-deposited with metal and abrasive as described previously.
The resulting abrasive layer has adhesive at both sides of the fabric material and surrounding the metal areas and can be readily adhered to a backing material by applying the backing material to the rear surface and heating to cause the adhesive to adhere the fabric material to the backing material. The adhesive is preferably a hot-melt adhesive, which is acid resistant and water repellant.
Other techniques for producing abrasive fabrics include the use of a fabric which is electrically conducting either by coating the fabric or fibres with metal or the use of metal fibres upon which metal is electro-deposited in a pattern-wise manner.
In principle, any metal, which may be electro-deposited, may be employed although in practice the metal is normally nickel. A wide range of abrasive particles may be embedded in the metal. Generally, the abrasive particles are diamond or synthetic boron nitride.
The abrasive layers comprising the mesh bearing the abrasive containing metal deposits, hereinafter referred to as xe2x80x9cabrasive fabricxe2x80x9d, is usually bonded to a backing member, for example, a backing sheet of woven material or a solid substrate. Adhesive present in the abrasive fabric may be employed to bond to the backing member and/or adhesive may be applied to the backing and/or the abrasive mesh, for example, by coating, spraying, dipping, lamination, etc.
In a known method, the abrasive fabric is bonded under heat and pressure to a polyester-cotton fabric backing utilizing a hot-melt polyester adhesive. The adhesive may be applied in the form of a separate film, which is commercially available on a release paper carrier or may be present on the surface of the polyester-cotton fabric.
The heat and pressure of the bonding operation causes the hot-melt adhesive to flow penetrating the abrasive fabric. This bonding technique has been used in respect of abrasive products in the form of discs, blocks, files, and pads. The other surface of this polyester-cotton fabric backing may be bonded to a block, pad, or provided with an attachment surface for attachment of the abrasive product to a suitable support.
According to a second known technique, a solution of a two-part, cross-linkable polyurethane adhesive is prepared and the abrasive fabric is completely immersed in the solution and thereafter removed and allowed to dry. This operation is generally repeated at least once to build up a satisfactory thickness of adhesive.
One side of a flexible cloth backing substrate is coated with the same adhesive solution and allowed to dry. At least one further coat is generally applied.
The backside of the abrasive fabric and adhesive coated side of the cloth are placed in contact and heat and pressure applied to effect a bond.
Products comprising abrasive mesh bonded to a backing have been commercially available since the mid-1980 under the Registered TradeMarks DIAPAD and 3M. The abrasive materials have been available in the form of belts, discs, pads, and blocks, etc. and have been employed for abrading a wide range of hard materials including metals, glass and stones, such as, granite, marble, etc. Under certain severe conditions of use, particularly at high temperatures, it has been found that the metal deposits may be delaminated from the backing; and in extreme cases, the fabric may tear resulting in metal deposit being removed from the abrasive material.
Various attempts have been made to enhance the bonding of the metal deposits to the backing. For example, primers such as 3M 901 Silane Primer, Loctite SIP (self-indicating primer), Bostick 9253 primer, and Ciba Geigy DZ81 acid etch primer have been employed with adhesive but any improvement in properties was found to be marginal. A range of different adhesives, for example, reactive polyurethanes, polyesters, rubber, nitrile rubber, polythene, and polychloroprene rubber, have been employed without significant improvement in properties.
It is an object of the present invention to provide abrasive materials comprising abrasive mesh which have improved delamination properties.
According to one embodiment of the present invention, there is provided an abrasive article comprising:
an abrasive fabric comprising a fabric having discrete areas of electro-deposited metal extending on or therethrough and having abrasive material embedded in the metal,
a layer of adhesive, and
a backing substrate, the abrasive fabric being bonded to the backing substrate by the layer of adhesive, characterized in that either (i) the surface of the abrasive fabric bonded to the backing has been roughened, for example, by abrading, and/or (ii) the layer of adhesive comprises an epoxy-acrylate thermosetting adhesive.
According to a second embodiment of the invention, there is provided a method of making an abrasive article comprising:
providing an abrasive fabric comprising a fabric having discrete areas of electro-deposited metal extending on or therethrough and having abrasive material embedded in the metal, and
bonding the abrasive fabric to a backing substrate with a layer of adhesive characterized in that prior to contacting the layer of adhesive the surface of the abrasive fabric is roughened, for example, by abrading.
According to a further embodiment of the invention, there is provided a method of making an abrasive article comprising:
providing an abrasive fabric comprising a fabric having discrete areas of electro-deposited metal extending on or therethrough and having abrasive material embedded in the metal, and
bonding the abrasive fabric to a backing substrate with a layer of adhesive characterized in that the layer of adhesive comprises an epoxy-acrylate thermosetting adhesive.
The products of the invention exhibit improved delamination resistance of the metal deposits which results in longer lifetime and improved cutting rates for the abrasive articles.